Method for estimating charge air cooler condensation storage and/or release with two intake oxygen sensors

ABSTRACT

Methods and systems are provided for estimating water storage in a charge air cooler (CAC). In one example, engine operation may be adjusted responsive to water storage parameters at the CAC, the water storage parameters based on an output of a first oxygen sensor positioned downstream of the CAC and a second oxygen sensor positioned upstream of the CAC. Further, operation of the first oxygen sensor and the second oxygen sensor may be diagnosed during certain engine operation conditions wherein no condensate is forming in the CAC.

BACKGROUND/SUMMARY

Turbocharged and supercharged engines may be configured to compressambient air entering the engine in order to increase power. Compressionof the air may cause an increase in air temperature, thus, anintercooler or charge air cooler (CAC) may be utilized to cool theheated air thereby increasing its density and further increasing thepotential power of the engine. Condensate may form in the CAC when theambient air temperature decreases, or during humid or rainy weatherconditions, where the intake air is cooled below the water dew point.Condensate may collect at the bottom of the CAC, or in the internalpassages, and cooling turbulators. Under certain air flow conditions,condensate may exit the CAC and enter an intake manifold of the engineas water droplets. If too much condensate is ingested by the engine,engine misfire and/or combustion instability may occur.

Other attempts to address engine misfire due to condensate ingestioninclude avoiding condensate build-up. In one example, the coolingefficiency of the CAC may be decreased in order to reduce condensateformation. However, the inventors herein have recognized potentialissues with such methods. Specifically, while some methods may reduce orslow condensate formation in the CAC, condensate may still build up overtime. If this build-up cannot be stopped, ingestion of the condensateduring acceleration may cause engine misfire. Additionally, in anotherexample, engine actuators may be adjusted to increase combustionstability during condensate ingestion. In one example, the condensateingestion may be based on a mass air flow rate and amount of condensatein the CAC; however, these parameters may not accurately reflect theamount of water in the charge air exiting the CAC and entering theintake manifold. As a result, engine misfire and/or unstable combustionmay still occur.

In one example, the issues described above may be addressed by a methodfor adjusting engine operation and generating diagnostics responsive towater storage parameters at a charge air cooler (CAC), the water storageparameters based on an output of a first oxygen sensor positioneddownstream of the charge air cooler and an output of a second oxygensensor positioned upstream of the charge air cooler. Specifically, thefirst oxygen sensor may be positioned at an outlet of the CAC and thesecond oxygen sensor may be positioned at an inlet of the CAC. Theoxygen sensors may be modulated between a variable voltage mode and abase mode at a rate based on exhaust gas recirculation (EGR) flow. Forexample, if EGR flow is greater than a threshold, the oxygen sensors mayoperate in the variable voltage mode for a shorter amount of time (e.g.,modulate more frequently) in order to measure oxygen content of thecharge air at the inlet and outlet of the CAC. An engine controller mayuse the outputs of the first oxygen sensor and the second oxygen sensorto determine water storage parameters at the CAC. In one example, thewater storage parameters may include one or more of a water releaseamount from the CAC, a water release rate from the CAC, a water storageamount in the CAC, and a water storage rate in the CAC. The enginecontroller may then adjust engine operation to increase combustionstability, decrease condensate formation in the CAC, and/or evacuatecondensate from the CAC in response to the determined water storageparameters. As a result, engine misfire and combustion instability dueto water ingestion may be decreased.

In another example, degradation of the first oxygen sensor and thesecond oxygen sensor may be indicated based on engine operatingconditions. Specifically, during engine operation when condensate lessthan a threshold is forming in the CAC and condensate less than athreshold is leaving the CAC, the engine controller may indicatedegradation of the first oxygen sensor and the second oxygen sensorbased on outputs of the first and second oxygen sensor relative to oneanother. Engine operation with condensate less than a threshold (e.g.,substantially no condensate) forming in and leaving the CAC may beidentified based on alternative condensate models and/or engineoperating conditions. During this engine operation, when the output ofthe first oxygen sensor is not within a threshold of the output of thesecond oxygen sensor, the controller may indicate degradation of one ormore of the first oxygen sensor and the second oxygen sensor. In thisway, function of the oxygen sensors may be diagnosed, thereby increasingaccuracy of the water storage parameter estimates.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example engine system including acharge air cooler.

FIG. 2 is a flow chart of a method for operating an oxygen sensor todetermine water storage at a charge air cooler.

FIG. 3 is a flow chart of a method for operating oxygen sensors todetermine water storage at a charge air cooler.

FIG. 4 is a flow chart of a method for adjusting engine operation basedon water storage at a charge air cooler.

FIG. 5 is a flow chart of a method for indicating degradation of a firstoxygen sensor positioned at an outlet of a CAC and a second oxygensensor positioned at an inlet of the CAC based on engine operatingconditions.

FIG. 6 shows a flow chart illustrating a method for inferring acondensate level at the charge air cooler.

FIGS. 7A-B show a graph illustrating example adjustments to engineoperation based on water storage at a charge air cooler.

DETAILED DESCRIPTION

The following description relates to systems and methods for estimatingwater storage in a charge air cooler (CAC) in an engine system, such asthe system of FIG. 1. A first oxygen sensor may be positioned at anoutlet of the CAC. In one example, the oxygen sensor may be a variablevoltage intake oxygen sensor which may operate between a variablevoltage (VVs) mode and a base mode. A method for operating the firstoxygen sensor to determine water storage at the CAC is shown in FIG. 2.Specifically, a water release amount, or amount of water in the chargeair at the CAC outlet, may be determined with the first oxygen sensor.In some examples, a second oxygen sensor may be positioned at an inletof the CAC. FIG. 3 shows a method for operating the first oxygen sensorand the second oxygen sensor to determine water storage parameters atthe CAC. The water storage parameters may include a water storage rate,a water release rate, a water storage amount (e.g., amount of water orcondensate within the CAC), and/or a water release amount. An enginecontroller may then adjust engine operation based on the water storageparameters, as shown at FIG. 4. Adjusting engine operation may includeadjusting engine actuators to decrease a cooling efficiency of the CAC,purge condensate from the CAC, and/or increase combustion stabilityduring ingestion of water by the engine. Additionally, as shown at FIGS.5-6, the engine controller may diagnose oxygen sensor function bycomparing the measurements and/or outputs of the first oxygen sensor andthe second oxygen sensor under certain engine operating conditions. Forexample, under engine operating conditions when no difference in theconcentration of oxygen is expected between the charge air entering andexiting the CAC, the controller may compare the oxygen sensor readings.If the difference in the sensor outputs is greater than a threshold, oneor more of the sensors may be degraded. In this way, positioning a firstoxygen sensor at the outlet of the CAC and/or a second oxygen sensor atthe inlet of the CAC may allow for the determination of condensatestorage parameters of the CAC. Engine actuator adjustments based onthese determined condensate storage parameters may then decreasecondensate formation in the CAC, increase combustion stability duringcondensate purging from the CAC, and/or decrease water storage withinthe CAC.

FIG. 1 is a schematic diagram showing an example engine 10, which may beincluded in a propulsion system of an automobile. The engine 10 is shownwith four cylinders or combustion chambers 30. However, other numbers ofcylinders may be used in accordance with the current disclosure. Engine10 may be controlled at least partially by a control system including acontroller 12, and by input from a vehicle operator 132 via an inputdevice 130. In this example, the input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Each combustion chamber (e.g.,cylinder) 30 of the engine 10 may include combustion chamber walls witha piston (not shown) positioned therein. The pistons may be coupled to acrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. The crankshaft 40 may becoupled to at least one drive wheel of a vehicle via an intermediatetransmission system 150. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10. The crankshaft 40 may also be used to drive an alternator (not shownin FIG. 1).

An engine output torque may be transmitted to a torque converter (notshown) to drive the automatic transmission system 150. Further, one ormore clutches may be engaged, including forward clutch 154, to propelthe automobile. In one example, the torque converter may be referred toas a component of the transmission system 150. Further, transmissionsystem 150 may include a plurality of gear clutches 152 that may beengaged as needed to activate a plurality of fixed transmission gearratios. Specifically, by adjusting the engagement of the plurality ofgear clutches 152, the transmission may be shifted between a higher gear(that is, a gear with a lower gear ratio) and a lower gear (that is, agear with a higher gear ratio). As such, the gear ratio differenceenables a lower torque multiplication across the transmission when inthe higher gear while enabling a higher torque multiplication across thetransmission when in the lower gear. The vehicle may have four availablegears, where transmission gear four (transmission fourth gear) is thehighest available gear and transmission gear one (transmission firstgear) is the lowest available gear. In other embodiments, the vehiclemay have more or less than four available gears. As elaborated herein, acontroller may vary the transmission gear (e.g., upshift or downshiftthe transmission gear) to adjust an amount of torque conveyed across thetransmission and torque converter to vehicle wheels 156 (that is, anengine shaft output torque).

As the transmission shifts to a lower gear, the engine speed (Ne or RPM)increases, increasing engine airflow. An intake manifold vacuumgenerated by the spinning engine may be increased at the higher RPM. Insome examples, as discussed further below, downshifting may be used toincrease engine airflow and purge condensate built up in a charge aircooler (CAC) 80.

The combustion chambers 30 may receive intake air from the intakemanifold 44 and may exhaust combustion gases via an exhaust manifold 46to an exhaust passage 48. The intake manifold 44 and the exhaustmanifold 46 can selectively communicate with the combustion chamber 30via respective intake valves and exhaust valves (not shown). In someembodiments, the combustion chamber 30 may include two or more intakevalves and/or two or more exhaust valves.

Fuel injectors 50 are shown coupled directly to the combustion chamber30 for injecting fuel directly therein in proportion to the pulse widthof signal FPW received from controller 12. In this manner, the fuelinjector 50 provides what is known as direct injection of fuel into thecombustion chamber 30; however it will be appreciated that portinjection is also possible. Fuel may be delivered to the fuel injector50 by a fuel system (not shown) including a fuel tank, a fuel pump, anda fuel rail.

In a process referred to as ignition, the injected fuel is ignited byknown ignition means such as spark plug 52, resulting in combustion.Spark ignition timing may be controlled such that the spark occursbefore (advanced) or after (retarded) the manufacturer's specified time.For example, spark timing may be retarded from maximum break torque(MBT) timing to control engine knock or advanced under high humidityconditions. In particular, MBT may be advanced to account for the slowburn rate. In one example, spark may be retarded during a tip-in. In analternate embodiment, compression ignition may be used to ignite theinjected fuel.

The intake manifold 44 may receive intake air from an intake passage 42.The intake passage 42 includes a throttle 21 having a throttle plate 22to regulate flow to the intake manifold 44. In this particular example,the position (TP) of the throttle plate 22 may be varied by thecontroller 12 to enable electronic throttle control (ETC). In thismanner, the throttle 21 may be operated to vary the intake air providedto the combustion chambers 30. For example, the controller 12 may adjustthe throttle plate 22 to increase an opening of the throttle 21.Increasing the opening of the throttle 21 may increase the amount of airsupplied to the intake manifold 44. In an alternate example, the openingof the throttle 21 may be decreased or closed completely to shut offairflow to the intake manifold 44. In some embodiments, additionalthrottles may be present in intake passage 42, such as a throttleupstream of a compressor 60 (not shown).

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from the exhaustpassage 48 to the intake passage 42 via an EGR passage, such as highpressure EGR passage 140. The amount of EGR provided to the intakepassage 42 may be varied by the controller 12 via an EGR valve, such ashigh pressure EGR valve 142. Under some conditions, the EGR system maybe used to regulate the temperature of the air and fuel mixture withinthe combustion chamber. FIG. 1 shows a high pressure EGR system whereEGR is routed from upstream of a turbine of a turbocharger to downstreamof a compressor of a turbocharger through EGR passage 140. FIG. 1 alsoshows a low pressure EGR system where EGR is routed from downstream ofturbine of a turbocharger to upstream of a compressor of a turbochargerthrough low pressure EGR passage 157. A low pressure EGR valve 155 maycontrol the amount of EGR provided to the intake passage 42. In someembodiments, the engine may include both a high pressure EGR and a lowpressure EGR system, as shown in FIG. 1. In other embodiments, theengine may include either a low pressure EGR system or a high pressureEGR system. When operable, the EGR system may induce the formation ofcondensate from the compressed air, particularly when the compressed airis cooled by the charge air cooler, as described in more detail below.

The engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 60 arrangedalong the intake passage 42. For a turbocharger, the compressor 60 maybe at least partially driven by a turbine 62, via, for example a shaft,or other coupling arrangement. The turbine 62 may be arranged along theexhaust passage 48. Various arrangements may be provided to drive thecompressor. For a supercharger, the compressor 60 may be at leastpartially driven by the engine and/or an electric machine, and may notinclude a turbine. Thus, the amount of compression provided to one ormore cylinders of the engine via a turbocharger or supercharger may bevaried by the controller 12.

In the embodiment shown in FIG. 1, the compressor 60 may be drivenprimarily by the turbine 62. The turbine 62 may be driven by exhaustgases flowing through the exhaust passage 48. Thus, the driving motionof the turbine 62 may drive the compressor 60. As such, the speed of thecompressor 60 may be based on the speed of the turbine 62. As the speedof the compressor 60 increases, more boost may be provided through theintake passage 42 to the intake manifold 44.

Further, the exhaust passage 48 may include a wastegate 26 for divertingexhaust gas away from the turbine 62. Additionally, the intake passage42 may include a compressor bypass or recirculation valve (CRV) 27configured to divert intake air around the compressor 60. The wastegate26 and/or the CRV 27 may be controlled by the controller 12 to be openedwhen a lower boost pressure is desired, for example. For example, inresponse to compressor surge or a potential compressor surge event, thecontroller 12 may open the CBV 27 to decrease pressure at the outlet ofthe compressor 60. This may reduce or stop compressor surge.

The intake passage 42 may further include a charge air cooler (CAC) 80(e.g., an intercooler) to decrease the temperature of the turbochargedor supercharged intake gases. In some embodiments, the CAC 80 may be anair to air heat exchanger. In other embodiments, the CAC 80 may be anair to liquid heat exchanger. The CAC 80 may also be a variable volumeCAC. Hot charge air (boosted air) from the compressor 60 enters theinlet of the CAC 80, cools as it travels through the CAC, and then exitsto pass through the throttle 21 and then enter the engine intakemanifold 44. Ambient air flow from outside the vehicle may enter engine10 through a vehicle front end and pass across the CAC, to aid incooling the charge air. Condensate may form and accumulate in the CACwhen the ambient air temperature decreases, or during humid or rainyweather conditions, where the charge air is cooled below the water dewpoint temperature. Further, when the charge air entering the CAC isboosted (e.g., boost pressure and/or CAC pressure is greater thanatmospheric pressure), condensate may form if the CAC temperature fallsbelow the dew point temperature. When the charge air includesrecirculated exhaust gasses, the condensate can become acidic andcorrode the CAC housing. The corrosion can lead to leaks between the aircharge, the atmosphere, and possibly the coolant in the case ofwater-to-air coolers. Further, if condensate builds up in the CAC, itmay be ingested by the engine during times of increased airflow. As aresult, unstable combustion and/or engine misfire may occur.

The engine 10 may further include one or more oxygen sensors positionedin the intake passage 42. As such, the one or more oxygen sensors may bereferred to as intake oxygen sensors. In the depicted embodiment, afirst oxygen sensor 162 is positioned downstream of the CAC 80. In oneexample, the first oxygen sensor 162 may be positioned at an outlet ofthe CAC 80. As such, the first oxygen sensor 162 may be referred toherein as the CAC outlet oxygen sensor. In another example, the firstoxygen sensor 162 may be positioned downstream of the CAC 80 outlet.FIG. 1 also shows a second oxygen sensor 160 positioned upstream of theCAC 80. In one example, the second oxygen sensor 160 may be positionedat an inlet of the CAC 80. As such, the second oxygen sensor 160 may bereferred to herein as the CAC inlet oxygen sensor. In another example,the second oxygen sensor 160 may be positioned upstream of the CAC inletand downstream of the compressor 60.

In some embodiments, the engine 10 may include both the first oxygensensor 162 and the second oxygen sensor 160. In other embodiments, theengine 10 may include only one of the first oxygen sensor 162 and thesecond oxygen sensor 160. For example, the engine 10 may only includethe first oxygen sensor 162 downstream of the CAC 80. In someembodiments, as shown in FIG. 1, an optional third oxygen sensor 164 maybe positioned in the intake passage 42. The third oxygen sensor 164 maybe positioned downstream of the compressor 60 and the EGR passage 140(or EGR passage 157 if the engine only includes low pressure EGR).

Intake oxygen sensors 160, 162, and/or 164 may be any suitable sensorfor providing an indication of the oxygen concentration of the chargeair (e.g., air flowing through the intake passage 42), such as a linearoxygen sensor, intake UEGO (universal or wide-range exhaust gas oxygen)sensor, two-state oxygen sensor, etc. In one example, the intake oxygensensors 160, 162, and/or 164 may be an intake oxygen sensor including aheated element as the measuring element. During operation, a pumpingcurrent of the intake oxygen sensor may be indicative of an amount ofoxygen in the gas flow.

In another example, the intake oxygen sensor 160, 162, and/or 164 may bea variable voltage (variable Vs or VVs) intake oxygen sensor wherein areference voltage of the sensor may be modulated between a lower or basevoltage at which oxygen is detected and a higher voltage at which watermolecules in the gas flow may be dissociated. For example, during baseoperation, the intake oxygen sensor may operate at the base referencevoltage. At the base reference voltage, when water hits the sensor, theheated element of the sensor may evaporate the water and measure it as alocal vapor or diluent. This operational mode may be referred to hereinas the base mode. The intake oxygen sensor may also operate in a secondmode wherein the reference voltage is increased to a second referencevoltage. The second reference voltage may be higher than the basereference voltage. Operating the intake oxygen sensor at the secondreference voltage may be referred to herein as variable Vs (VVs) mode.When the intake oxygen sensor operates in VVs mode, the heated elementof the sensor dissociates water in the air and subsequently measures thewater concentration. In this mode, the pumping current of the sensor maybe indicative of an amount of oxygen in the gas flow plus an amount ofoxygen from dissociated water molecules. However, if the referencevoltage is further increased, additional molecules, such as CO₂, mayalso be dissociated and the oxygen from these molecules may also bemeasured by the sensor. In a non-limiting example, the lower, basereference voltage may be 450 mV and the higher, second reference voltagemay be greater than 950 mV. However, in the methods presented at FIGS.2-3 for determining an amount of water in the charge air, the secondreference voltage may be maintained lower than a voltage at which CO₂may also be dissociated. In this way, the second reference voltage maybe set such that only oxygen from water (and not CO₂) may be measured inVVs mode.

The first oxygen sensor 162 and/or the second oxygen sensor 160 may beused to estimate condensate or water storage at the CAC 80 and/or waterrelease from the CAC 80. As discussed further below with reference toFIGS. 2-3, the oxygen concentration in the air entering and/or leavingthe CAC 80 (e.g., determined by second oxygen sensor 160 and firstoxygen sensor 162, respectively) may be used to determine aconcentration of water entering and/or leaving the CAC 80. Variousmethods may be used to estimate water in the charge air entering and/orleaving the CAC 80. For example, the intake oxygen sensor(s) may measurean amount of oxygen in the charge air and then estimate an amount ofwater in the charge air using a dilution method. If the intake oxygensensor is a VVs intake oxygen sensor, the sensor may estimate an amountof water in the charge air using a dissociation method (e.g., operatingin VVs mode and modulating between a base reference voltage and ahigher, second reference voltage). Both of these methods for measuringand/or estimating an amount of water in the charge air are discussedfurther below.

A first method for estimating water in the charge air using an intakeoxygen sensor includes the dilution method. When using the dilutionmethod, the intake oxygen sensor may be operated in the base mode at thebase reference voltage. In one example, the base reference voltage maybe 450 mV. In another example, the base reference voltage may be avoltage larger or smaller than 450 mV. The intake oxygen sensor may takea measurement and determine an amount of oxygen in the gas (e.g., intakeor charge air) based on a pumping current of the sensor. Then, acomparison of the measured concentration of oxygen vs. the amount of airmay be used to determine the amount of water as a diluent in the chargeair. The dilution method may give an inaccurate water estimate if thediluent includes substances other than water, such as EGR and/or fuelvapor.

A second method for estimating water in the charge air using an intakeoxygen sensor includes the dissociation method. Specifically, for thedissociation method, a VVs intake oxygen sensor may operate in VVs modewherein the reference voltage is increased from the base referencevoltage to the higher, second reference voltage. In one example, thesecond reference voltage may be 950 mV. In another example, the secondreference voltage may be a voltage greater than 950 mV. However, thesecond reference voltage may be maintained at a voltage lower than thevoltage at which CO₂ is dissociated by the sensor. In VVs mode, theintake oxygen sensor dissociates the water into hydrogen and oxygen andmeasures the amount of oxygen from dissociated water molecules inaddition to the amount of oxygen in the gas. By taking the differencebetween the measurements at the second reference voltage and the basereference voltage, an estimate of the total water concentration in thecharge air may be determined. Additionally, at each temperaturecondition at the outlet of the CAC, a different amount of saturatedwater may be produced. If the saturation water at the CAC outlettemperature condition is known (e.g., in a look-up table stored in thecontroller), the controller 12 may subtract this value from the totalwater concentration measured by the intake oxygen sensor to determine anamount water in the charge air in the form of water droplets. Forexample, the saturation water at the CAC outlet temperature conditionmay include a mass of water at the saturation vapor pressure conditionat the CAC outlet. In this way, the controller may determine an amountof liquid water in the charge air entering and/or exiting the CAC fromintake oxygen sensor measurements.

In order to determine the total water concentration at the oxygensensors, the oxygen sensors may be modulated between the base and theVVs mode reference voltages. The length or pulse width of the modulationmay be based on an amount of diluents (other than water) in the air. Inone example, the other diluent may be EGR. For example, as EGRincreases, the amount of diluents in the air increases. As a result, theoxygen concentration measured in the base mode may decrease while theamount of dissociated oxygen measured in VVs mode may increase. Thus, anet measurement between the two reference voltages may be required moreoften in order to increase the accuracy of water concentrationmeasurements. Thus, as EGR increases (e.g., an EGR amount or EGR flowrate), the pulse width between the two reference voltages may decrease.In this way, VVs mode may be run for a shorter amount of time than whenthe EGR is at a lower flow rate. In one example, the pulse width betweenthe base voltage and the second voltage (e.g., VVs voltage) may be evensuch that the same amount of time is spent in each voltage. In a secondexample, the pulse width may be uneven such that the sensor spends alonger amount of time in one mode than the other. In this case, thepulse width may be a first pulse width of the VVs mode and a secondpulse width of the base mode. In some examples, if EGR is relativelyhigh and above a threshold, there may be an even on/off time between theVVs and base mode such that the first pulse width and the second pulsewidth are the same. These two pulse widths may be shorter than if theEGR was below the threshold. In yet another example, if there is no EGRin the charge air (EGR flow is substantially zero), the oxygen sensormay operate for a longer time in VVs mode or may operate only in VVsmode until the EGR flow increases. In this example, the oxygen sensormay not modulate between modes.

The controller 12 may use measurements at one or both of the firstoxygen sensor 162 and the second oxygen sensor 160 to determine one ormore of a water storage rate in the CAC 80, a water release rate fromthe CAC 80, a water storage amount in the CAC 80 (e.g., amount of waterin the CAC 80), and/or a water release amount from the CAC 80 (e.g.,amount or volume of water leaving the CAC 80 and traveling to the intakemanifold 44). For example, the water release amount from the CAC 80 maybe estimated from measurements from the first oxygen sensor 162positioned at the CAC outlet. The controller 12 may determine the waterrelease amount by one or more of the methods described above (e.g.,dilution or dissociation method). In another example, the water storagerate in the CAC 80 and/or the water release rate from the CAC 80 may bedetermined by comparing measurements of the first oxygen sensor 162 andthe second oxygen sensor 160. Specifically, if the determined waterconcentration (or estimated amount of water) at the first oxygen sensor162 is greater than the determined water concentration (or estimatedamount of water) at the second oxygen sensor 160 water is leaving theCAC 80. Thus, the water release rate from the CAC 80 may be based on adifference between the water measurements at the first oxygen sensor 162and the second oxygen sensor 160. Conversely, if the determined waterconcentration (or estimated water amount) at the second oxygen sensor160 is greater than the determined water concentration (or estimatedwater amount) at the first oxygen sensor 162, water is being stored inthe CAC 80. Thus, the water storage rate at the CAC 80 may be based on adifference between the water measurements at the second oxygen sensor160 and the second oxygen sensor 162. Further, by integrating the waterstorage and/or water release rate, the controller 12 may estimate theamount of water being stored within the CAC 80 (e.g., water storageamount).

In response to these water storage estimates, the controller 12 mayadjust engine actuators to adjust combustion parameters, activatecondensate purging routines, and/or adjust actuators to increase ordecrease CAC cooling efficiency. Engine actuator adjustments in responseto water storage measurements from the oxygen sensors is presented infurther detail below at FIG. 4.

The third oxygen sensor 164 may be used to determine EGR flow. Forexample, controller 12 may estimate the percent dilution of the EGR flowbased on feedback from the third oxygen sensor 164. In some examples,the controller 12 may then adjust one or more of EGR valve 142, EGRvalve 155, throttle 21, CRV 27, and/or wastegate 26 to achieve a desiredEGR dilution percentage of the intake air. In other examples, EGR flowmay be determined from one or both of the first oxygen sensor 162 andthe second oxygen sensor 160.

The controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. The controller 12 may receivevarious signals from sensors coupled to the engine 10 for performingvarious functions to operate the engine 10. In addition to those signalspreviously discussed, these signals may include measurement of inductedmass air flow from MAF sensor 120; engine coolant temperature (ECT) fromtemperature sensor 112, shown schematically in one location within theengine 10; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; the throttleposition (TP) from a throttle position sensor, as discussed; andabsolute manifold pressure signal, MAP, from sensor 122, as discussed.Engine speed signal, RPM, may be generated by the controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold 44. Note that various combinations of the above sensorsmay be used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, the Hall effect sensor 118, which is alsoused as an engine speed sensor, may produce a predetermined number ofequally spaced pulses every revolution of the crankshaft 40.

Other sensors that may send signals to controller 12 include atemperature and/or pressure sensor 124 at an outlet of a charge aircooler 80, the first oxygen sensor 162, the second oxygen sensor 160,the third oxygen sensor 164, and a boost pressure sensor 126. Othersensors not depicted may also be present, such as a sensor fordetermining the intake air velocity at the inlet of the charge aircooler, and other sensors. In some examples, storage medium read-onlymemory chip 106 may be programmed with computer readable datarepresenting instructions executable by microprocessor unit 102 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed. Example routines aredescribed herein at FIGS. 2-6.

The system of FIG. 1 provides for an engine system including an intakemanifold, a charge air cooler positioned upstream of the intakemanifold, a first oxygen sensor positioned at an outlet of the chargeair cooler, a second oxygen sensor positioned at an inlet of the chargeair cooler, and a controller with computer readable instructions foradjusting engine operation responsive to water storage parameters at thecharge air cooler, the water storage parameters based on an output ofthe first oxygen sensor and an output of the second oxygen sensor. Inone example, adjusting engine operation includes one or more ofadjusting spark timing, mass air flow, vehicle grille shutters, enginecooling fans, a charge air cooler coolant pump, and/or downshifting atransmission gear. Further, water storage parameters include one or moreof a water release amount from the charge air cooler, a water releaserate from the charge air cooler, a water storage amount in the chargeair cooler, and a water storage rate in the charge air cooler. In analternate embodiment, the engine system may not include the secondoxygen sensor. In this embodiment, the controller may include computerreadable instructions for adjusting engine actuators based on an amountof water in charge air exiting the charge air cooler, the amount ofwater based on an output of the first oxygen sensor.

FIG. 2 shows a method 200 for operating an oxygen sensor to determinewater storage at the CAC. Specifically, the oxygen sensor may be anoxygen sensor positioned proximate to an outlet of the CAC. In oneexample, the method 200 is executable by the controller 12 shown inFIG. 1. The method 200 may be used in an engine system in which only anoxygen sensor at the outlet of the CAC (such as first oxygen sensor 162shown in FIG. 1) is used to determine water storage parameters at theCAC. For example, the engine system may not have an oxygen sensorpositioned at the inlet of the CAC (such as second oxygen sensor 160shown in FIG. 1).

The method begins at 202 by estimating and/or measuring engine operatingconditions. Engine operating conditions may include engine speed andload, EGR flow rate, mass air flow rate, conditions of the charge aircooler (e.g., inlet and/or outlet temperature and pressures), humidity,ambient temperature, torque demand, etc. At 204, the method includesmodulating the reference voltage of the oxygen sensor between a firstvoltage and a second voltage at a pulse width based on an amount ofdiluent in the charge air. The first voltage may also be referred toherein as a base voltage. As one non-limiting example, the first voltagemay be 450 mV and the second voltage may be 950 mV. At 450 mV, forexample, the pumping current may be indicative of an amount of oxygen inthe charge air (e.g., air exiting the CAC). At 950 mV, water moleculesmay be dissociated such that the pumping current is indicative of theamount of oxygen in the charge air plus an amount of oxygen fromdissociated water molecules. The first voltage may be a voltage at whicha concentration of oxygen in the charge air may be determined, forexample, while the second voltage may be a voltage at which watermolecules may be dissociated.

In one example, the amount of diluent in the charge air may be an amountof EGR in the charge air. The amount of EGR in the charge air may bebased on an EGR flow rate. In another example, the amount of diluent inthe charge air may be an amount of another type of diluent in the chargeair other than water and EGR. As discussed above, as EGR increases, thepulse width of the modulation between the first and second referencevoltages may decrease. In this way, the oxygen sensor may spend ashorter amount of time at the second, higher reference voltage. As such,a more accurate net measurement between the two reference voltages maybe obtained, thereby giving a more accurate water concentrationmeasurement, as discussed further below.

At 206, the method includes determining a change in pumping currentduring the modulation. For example, the difference in pumping current atthe first reference voltage and the pumping current at the secondreference voltage is determined. As described above, the change inpumping current may be indicative of the amount of oxygen in the gas andthe amount of oxygen dissociated from water molecules in the gas (e.g.,charge air).

From 206, the method proceeds to 208 to determine a total water (e.g.,condensate) concentration in the charge air (e.g., in the charge air atthe CAC outlet) based on the change in pumping current. Then, at 210,the method includes determining an amount of liquid water (e.g., waterdroplets) in the charge air at the CAC outlet (e.g., exiting the CAC).This water amount may be a water release amount from the CAC. The methodat 210 may include subtracting a saturation water value for the CACoutlet temperature from the total water concentration. The saturationwater values may include a mass of water at the saturation vaporpressure condition at the CAC outlet. As discussed above, the controllermay determine the saturation water value from a look-up table ofsaturation water values at various CAC outlet temperatures stored in thecontroller. At 212, the controller may adjust engine actuators based onthe water release amount determined at 210 and/or the water releaseamount inferred from the total water concentration determined at 208. Amethod for adjusting engine actuators responsive to the water releaseamount is presented at FIG. 4.

In some embodiments, if EGR flow is substantially zero, the oxygensensor may operate only in VVs mode without modulating between the tworeference voltages. As such, any extra oxygen determined at the sensormay be due to water vapor. In this example, the water release from theCAC may be determined based on this measurement and then used to adjustengine actuators, as described at 212.

In this way, a method may include adjusting engine operation responsiveto water content in an intake system, the water content based on anoutput of an intake oxygen sensor wherein a reference voltage of theintake oxygen sensor is adjusted between a first voltage and a secondvoltage at a higher rate as an exhaust gas recirculation flow increases.As described above, an oxygen sensor may be positioned within an intakesystem (e.g., intake passage 42 and/or intake manifold 44 shown in FIG.1). In one example, the intake oxygen sensor may be positioned at a CACinlet or outlet. In another example, the intake oxygen sensor may bepositioned at another location in the intake system such as downstreamor upstream of the CAC. A reference voltage of the intake oxygen sensormay be adjusted, or modulated, between a first voltage and a secondvoltage, the second voltage being greater than the first voltage. Thefirst voltage may be a voltage at which a concentration of oxygen in theintake air may be determined, for example, while the second voltage maybe a voltage at which water molecules may be dissociated. A differencein a pumping current of the intake oxygen sensor at the first voltageand second voltage may be indicative of water content in the intakesystem. Engine operation, such as spark timing, airflow, etc., may thenbe adjusted response to the water content determined at the intakeoxygen sensor.

As described above, the reference voltage of the intake oxygen sensormay be adjusted or switched between the first voltage and the secondvoltage and a certain rate. By increasing the rate of adjusting orswitching between the first voltage and the second voltage, the intakeoxygen sensor may spend less time at one voltage. As exhaust gasrecirculation flow (e.g., flow rate) increases, the rate of switchingbetween the first voltage and the second voltage may increase toincrease the accuracy of the water content measurement. Thus, when theEGR flow is at a first, lower flow, the rate of adjusting between thefirst voltage and the second voltage may be at a first, lower rate.Then, when the EGR flow is at a second, higher flow, the rate ofadjusting between the first voltage and the second voltage may be at asecond, higher rate. As described above, the intake oxygen sensor mayoperate in a base mode when the reference voltage is at the firstvoltage and the intake oxygen sensor may operate in a VVs mode when thereference voltage is at a higher, second voltage.

FIG. 3 shows a method 300 for operating oxygen sensors to determinewater storage at the CAC. Specifically, the oxygen sensors may be afirst oxygen sensor positioned proximate to an outlet of the CAC (e.g.,outlet oxygen sensor) and a second oxygen sensor positioned proximate toan inlet of the CAC (e.g., inlet oxygen sensor). In one example, themethod 300 is executable by the controller 12 shown in FIG. 1. Themethod 300 may be used in an engine system in which the first oxygensensor at the outlet of the CAC (such as first oxygen sensor 162 shownin FIG. 1) and/or the second oxygen sensor at the inlet of the CAC (suchas second oxygen sensor 160 shown in FIG. 1) are used to determine waterstorage parameters at the CAC.

The method begins at 302 by estimating and/or measuring engine operatingconditions. Engine operating conditions may include engine speed andload, EGR flow rate, mass air flow rate, conditions of the charge aircooler (e.g., inlet and/or outlet temperature and pressures), humidity,ambient temperature, torque demand, etc. At 304, the method includesmodulating the reference voltage of the oxygen sensors between a firstvoltage (e.g., base voltage) and a second voltage at a pulse width basedon an amount of diluent in the charge air. The second voltage is higherthan the first voltage. As one non-limiting example, the first voltagemay be 450 mV and the second voltage may be 950 mV. As discussed abovewith reference to FIG. 2, the amount of diluent in the charge air may bean amount of EGR in the charge air, the amount of EGR in the charge airbased on an EGR flow rate. In another example, the amount of diluent inthe charge air may be an amount of another type of diluent in the chargeair other than water and EGR. As EGR increases, the pulse width of themodulation between the first and second reference voltages may decrease.In one embodiment, the pulse width of the inlet oxygen sensor and thepulse width of the outlet oxygen sensor may be the same. In anotherembodiment, the pulse width of the inlet oxygen sensor and the pulsewidth of the outlet oxygen sensor may not be the same. In thisembodiment, the different pulse widths may be based on EGR, as well ascondensation at the CAC.

At 306, the method includes determining a change in pumping current ateach of the inlet oxygen sensor and the outlet oxygen sensor during themodulation. For example, the difference in pumping current at the firstreference voltage and the pumping current at the second referencevoltage is determined.

The method at 307 includes estimating the water release amount from theCAC based on the output of the oxygen sensor positioned at the CACoutlet (e.g., outlet oxygen sensor). Operating the oxygen sensors andestimating the water release amount from the outlet oxygen sensor mayfollow the same procedure as outlined above at steps 206-210 in method200 of FIG. 2. As described above, the water release amount may be basedon a change in pumping current, as well as a saturation water value atthe CAC outlet temperature condition. The CAC outlet temperaturecondition may be determined from a temperature sensor positioned at theoutlet of the CAC (such as sensor 124 shown in FIG. 1).

At 308, the controller may compare the outputs or measurements of theinlet oxygen sensor and the outlet oxygen sensor to determine a waterrelease or water storage rate. In one example, comparing the sensoroutputs may include taking the difference between the water estimates.The water estimates may include an amount of liquid water in the chargeair, as described above. In another example, the water estimates mayinclude a total amount of water in the charge air (e.g., total waterconcentration). In this example, the saturation water value at the CACoutlet temperature may not be subtracted from this amount, as shown at210 in FIG. 2. In yet another example, the water estimates may includewater estimates based on the pumping current at the higher, secondreference voltage alone (and not the change in pumping current whenincreasing the reference voltage) if the EGR flow is substantially zero.The controller may subtract the water estimate of the outlet oxygensensor from the water estimate of the inlet oxygen sensor. If thedifference in the water estimates is positive, water may be being storedwithin the CAC and the difference in the water estimates is a waterstorage rate of the CAC. Alternatively, if the difference in the waterestimates is negative, water may be being released from the CAC and thedifference in the water estimates is a water release rate from the CAC.

After determining the water release rate or water storages rate, themethod continues on to 310 to determine a water storage amount. In oneexample, the method at 310 may include integrating the water releaseand/or water storage rate to determine the water storage amount. Thewater storage amount may be an amount of water or condensate storedwithin the CAC. The water storage amount may increase ascondensate-forming conditions increase. Condensate forming conditionsmay include increasing ambient humidity and/or decreasing ambienttemperature.

At 312, the controller may adjust engine actuators based on thedetermined water release amount, water storage amount, water releaserate, and/or water storage rate. In one example, the controller mayadjust engine actuators to decrease a cooling efficiency of the CAC asthe water storage amount increases. In another example, the controllermay adjust engine actuators to purge condensate from the CAC as waterstorage increases. In yet another example, the controller may adjustengine actuators to increase combustion stability as the water releaserate and/or water release amount increases. A method for adjustingengine actuators based on the water release amount, water storageamount, water release rate, and/or water storage rate at the CAC ispresented at FIG. 4, described further below.

Turning now to FIG. 4, a method 400 is shown for adjusting engineactuators and/or engine operation based on water storage in the CAC. Inone example, the method 400 is executable by the controller 12 shown inFIG. 1. Method 400 begins at 402 by obtaining oxygen sensor data fromone or more oxygen sensors. The one or more oxygen sensors may includean oxygen sensor proximate to the inlet of the CAC (e.g., second oxygensensor 160 shown in FIG. 1) and/or an oxygen sensor positioned proximateto the outlet of the CAC (e.g., first oxygen sensor 162 shown in FIG.1). For example, the method at 402 may include obtaining CAC waterstorage data or parameters determined in method 200 or method 300,presented at FIG. 2 and FIG. 3, respectively. The water storageparameters may include one or more of a water storage rate (e.g., rateof water accumulating within the CAC), a water storage amount (e.g.,amount of water stored in the CAC), a water release rate (e.g., rate ofwater exiting the CAC in the charge air stream), and/or a water releaseamount (e.g., amount of water in the charge air exiting the CAC).

At 404, the method includes determining if the water storage rate (e.g.,condensate storage rate) is greater than a threshold rate. In oneexample, the threshold water storage rate may be based on a rate atwhich a threshold amount of condensate may accumulate in the CAC. Thethreshold amount of condensate (or water) may result in engine misfireor unstable combustion if blown out of the CAC at once and ingested bythe engine. If the water storage rate is greater than the thresholdrate, the method continues on to 406 to decrease cooling efficiency ofthe CAC. Decreasing cooling efficiency of the CAC may include one ormore of closing or reducing an opening of vehicle grille shutters,turning off or reducing a speed of an engine cooling fan or dedicatedCAC fan, and/or decreasing coolant pump speed of a coolant-cooled CAC.Other engine actuator adjustments may also be made to decrease thecooling efficiency of the CAC, thereby reducing condensate formation. Inone example, the controller may adjust the above engine actuators (e.g.,fan, grille shutters, etc.) to increase the CAC temperature above a dewpoint temperature.

After decreasing CAC cooling efficiency, the method continues on to 408to determine if a water storage amount at the CAC is greater than athreshold amount. As discussed above, the water storage amount may be anamount of condensate or water stored or built-up within the CAC. In oneexample, the threshold water storage amount may be based on an amount ofwater that may result in engine misfire and/or unstable combustion ifblown out of the CAC and ingested by the engine all at once. If thewater storage amount at the CAC is greater than the threshold amount,the method continues on to 410 to purge accumulated condensate from theCAC. At 410, the controller may activate various condensate purgingroutines to evacuate condensate from the CAC, based on engine operatingconditions. For example, during a tip-in or other increase in engineairflow, the controller may limit an increase in engine airflow tocontrollably release condensate from the CAC and into the intakemanifold of the engine. In another example, the controller may increaseengine airflow, even if there is not an increased torque request, topurge condensate from the CAC. In one example, the controller mayincrease engine airflow by downshifting at transmission gear. In anotherexample, increasing engine airflow may include increasing an opening ofa throttle to increase mass air flow. The method at 410 may also includeadjusting additional engine actuators such as spark timing, air-fuelratio, etc. during the various condensate purging routines.Alternatively, if the water storage amount is not greater than thethreshold amount at 408, the method may continue on to 412 to maintainengine airflow at a requested level and maintain engine operatingconditions.

Returning to 404, if the water storage rate is not greater than thethreshold rate, the method continues on to 414 to determine if the waterrelease rate is greater than threshold rate and/or if the water releaseamount from the CAC is greater than a threshold amount. The thresholdwater release rate and/or the threshold amount of water release may bebased on an amount of water that may cause unstable combustion and/orengine misfire when ingested by the engine. If either of the conditionsat 414 is met, the method continues on to 416 to adjust combustionparameters and/or limit airflow to the engine. In one example, adjustingcombustion parameters may include adjusting spark timing to increasecombustion stability during the water ingestion (e.g., water releasefrom CAC). For example, the controller may advance spark timing during atip-in when the water release rate and/or water release amount aregreater than their respective thresholds. In another example, thecontroller may retard spark timing if the pedal position is relativelyconstant, or below a threshold position, when the water release rateand/or water release amount are greater than their respective thresholds(e.g., during a condensate purging routine). The amount of spark retardor advance may be based on the water release rate and/or the waterrelease amount. In other examples, additional or alternative combustionparameters may be adjusted during the water release conditions.

If the water release rate and the water release amount are not greaterthan their respective thresholds at 414, the method continues on to 412to maintain engine operating conditions. In alternate embodiments, themethod after 414 may also include determining if the water storageamount in the CAC is greater than the threshold amount (as shown at408). In this embodiment, the method may continue directly from 414 to408 and then continue on as described above.

In this way, the controller may adjust engine actuators to reducecondensate formation at the CAC and/or increase combustion stabilityduring water release from the CAC. The controller may base the engineactuator adjustments on water storage and/or water release (e.g., amountof water in the charge air exiting the CAC) parameters. Further, thecontroller may determine the CAC water storage and/or water releaseparameters based on output from one or more oxygen sensors positionedaround the CAC (e.g., at the inlet and/or outlet of the CAC).

In addition to controlling CAC cooling efficiency and/or combustionparameters, outputs from the inlet and outlet CAC oxygen sensors may beused for various diagnostics. In one example, the controller may useoxygen sensor output to diagnose alternate models and/or estimates ofCAC efficiency, CAC condensate, and/or CAC dew point. For example, awater storage rate (or amount) determined from the inlet and outlet CACoxygen sensors may be compared to an expected water storage ratedetermined from one of the CAC condensate models. If the two waterstorage rate estimates are not within a threshold of one another, thecontroller may indicate an error in the condensate model. The controllermay then make adjustments to the model to increase the accuracy. Adescription of example CAC condensate estimates and/or models aredescribed below with regard to FIGS. 5-6.

In another example, the controller may diagnose oxygen sensor functionby comparing the measurements and/or outputs of the CAC inlet and outletoxygen sensors under certain operating conditions. For example, underengine operating conditions when no difference in the concentration ofoxygen is expected between the charge air entering and exiting the CAC,the controller may compare the oxygen sensor readings. If there is adifference in the oxygen concentration measurements between the inletoxygen sensor and the outlet oxygen sensor, the controller may determinethat one or both of the sensors is degraded. The engine operatingconditions for diagnosing the inlet and outlet oxygen sensors mayinclude one or more of no EGR flow (or EGR flow rate below a threshold)and no net change in condensation at the CAC. For example, no net changein condensation at the CAC may include no condensate forming in orleaving the CAC (e.g., a water storage rate and water release rate ofsubstantially zero).

FIG. 5 shows a method 500 for indicating degradation of a first oxygensensor positioned at an outlet of a CAC and a second oxygen sensorpositioned at an inlet of the CAC based on engine operating conditions.In alternate embodiments, the first oxygen sensor may be positioneddownstream of the CAC and upstream of combustion chambers of the engineand the second oxygen sensor may be positioned upstream of the CAC anddownstream of a compressor. In one example, the method 500 is executableby the controller 12 shown in FIG. 1. Further, the first oxygen sensormay be referred to as the outlet oxygen sensor and the second oxygensensor may be referred to as the inlet oxygen sensor.

The method begins at 502 by estimating and/or measuring engine operatingconditions. Engine operating conditions may include engine speed andload, EGR flow rate, mass air flow rate, conditions of the charge aircooler (e.g., inlet and/or outlet temperatures and pressures), humidity,ambient temperature, torque demand, etc. At 504, the method includesdetermining the level or amount of condensate in the CAC. This mayinclude retrieving details such as ambient air temperature, ambient airhumidity, inlet and outlet charge air temperature, inlet and outletcharge air pressure, and air mass flow rate from a plurality of sensorsand determining the amount of condensate formed in the CAC based on theretrieved data. In one example, at 506, and as further elaborated at themodel of FIG. 6, the rate of condensate formation within the CAC may bebased on ambient temperature, CAC outlet temperature, mass flow, EGR,and humidity. In another example, at 508, a condensation formation valuemay be mapped to CAC outlet temperature and a ratio of CAC pressure toambient pressure. In an alternate example, the condensation formationvalue may be mapped to CAC outlet temperature and engine load. Engineload may be a function of air mass, torque, accelerator pedal position,and throttle position, and thus may provide an indication of the airflow velocity through the CAC. For example, a moderate engine loadcombined with a relatively cool CAC outlet temperature may indicate ahigh condensation formation value, due to the cool surfaces of the CACand relatively low intake air flow velocity. The map may further includea modifier for ambient temperature.

At 510, the method includes determining if no condensate is forming inthe CAC and no condensate is leaving the CAC. In an alternate example,the method at 510 may include determining if condensate below athreshold is forming in the CAC and if condensate below the threshold isleaving the CAC. In one example, the threshold may be substantially zerosuch that no condensate is forming in and leaving the CAC. In anotherexample, the threshold may be a condensate level or rate greater thanzero. Thus, in one example, the method at 510 may include determining ifthe amount and/or rate of condensate formation, as determined at 504,are substantially zero. In another example, the method at 510 mayinclude determining if the amount and/or rate of condensate formationare less than a threshold. As discussed above, the threshold mayindicate no net condensate formation at the CAC. The method at 510 mayalso include determining if the condensate release rate (e.g., waterrelease rate) and/or condensate release amount (e.g., water releaseamount) are less than a threshold. The condensate release rate and/orrelease amount may be based on one or more of the determined level ofcondensate in the CAC, mass air flow, humidity, CAC temperature, etc.For example, if the condensate level in the CAC is below a thresholdand/or the mass air flow is below a flow threshold for purgingcondensate, the controller may infer the condensate release rate to besubstantially zero.

If the controller determines that condensate is forming in the CACand/or condensate is leaving the CAC, the method continues on to 512 tonot diagnose the oxygen sensors. The method may return to the beginningof the method and wait until the conditions at 510 are fulfilled.Alternatively, if the controller determines that no condensate isforming in the CAC and no condensate is leaving (e.g., being purgedfrom) the CAC, the method continues on to 514. At 514, the methodincludes determining if the EGR flow rate is less than a threshold. Inone example, the threshold EGR flow rate may be substantially zero. Assuch, oxygen sensor diagnosis may only proceed if there is no EGR. Inanother example, the threshold EGR flow rate may be a rate greater thanzero but small enough such that the EGR flow may not cause a differencein the oxygen sensor output (e.g., oxygen concentration) between theinlet oxygen sensor and the outlet oxygen sensor. If EGR is not belowthe threshold at 514, the method continues on to 512 to not diagnose theoxygen sensors. The method may then return to the beginning.

However, if the EGR is below the threshold at 514, the method continueson to 516 to acquire oxygen sensor outputs at the CAC outlet oxygensensor (OS) and inlet oxygen sensor (IS). Oxygen sensor output data mayinclude one or more of an oxygen concentration obtained via thedissociation method when the oxygen sensors are operating in VVs mode(modulating between the first reference voltage and the second referencevoltage) and/or an oxygen concentration obtained via the dilution methodwhen the oxygen sensors are operating in the base mode, as describedabove. Both the inlet oxygen sensor and the outlet oxygen sensor may beoperated in the same mode when obtaining sensor data for oxygen sensordiagnosis at 516.

At 518, the method includes determining if the concentration of oxygenestimated at the outlet oxygen sensor is within a threshold of theconcentration of oxygen estimated at the inlet oxygen sensor. Inalternate embodiments, a different type of oxygen sensor output otherthan oxygen concentration (e.g., pumping current) may be compared at518. The threshold may be pre-set and be based on a desired percentageaccuracy or accuracy tolerance of the sensors. If both sensor readingsare within the threshold of one another, the method continues on to 520to determine the oxygen sensors are not degraded. Oxygen sensoroperation for determining condensate storage parameters and adjustingengine actuators in response to condensate storage parameters may thencontinue as discussed above.

Alternatively at 518, if the concentration of oxygen measured by theoutlet oxygen sensor and the concentration of oxygen measured by theinlet oxygen sensor are not within a threshold of one another, themethod continues on to 522. At 522, the controller may indicate apossible degradation of oxygen sensor function. The method at 522 mayinclude zeroing and/or resetting both the inlet and outlet oxygen sensorand then re-measuring the oxygen in the charge air at the inlet andoutlet of the CAC. At 524, the controller determines if the new oxygenconcentration estimate at the outlet oxygen sensor is within a thresholdof the new oxygen concentration estimate at the inlet oxygen sensor. Inone example, the threshold at 524 and the threshold at 518 may be thesame. In another example, the threshold at 524 may be smaller or largerthan the threshold at 518. If the new oxygen concentration measurementsat the inlet and outlet oxygen sensors are within the threshold of oneanother, the method continues on to 520 to determine that the sensorsare not degraded and continue oxygen sensor operation. However, if theoxygen concentration determined at the outlet oxygen sensor is notwithin the threshold of the oxygen concentration determined at the inletoxygen sensor, the controller may determine that one or more of theinlet oxygen sensor and the outlet oxygen sensor are degraded at 526. Inone example, at 526 the controller may notify the vehicle operator thatmaintenance of the oxygen sensors is required.

In some embodiments, method 500 may include a step before 502determining if it is time to perform sensor diagnostics. In one example,the sensor diagnostics (e.g., method 500) may be executed by thecontroller after a duration of engine operation since the last sensordiagnostic. The duration may be a pre-set value. Alternatively, sensordiagnostics may be performed ever time sensor diagnostic conditions aremet. As described above at 510 and 514, sensor diagnostic conditions mayinclude no condensate forming in or leaving the CAC, and an EGR flowrate below a threshold.

In this way, during engine operation when condensate less than athreshold is forming in a charge air cooler and condensate less than thethreshold is leaving the charge air cooler, an engine method may includeindicating degradation of a first oxygen sensor positioned downstream ofthe charge air cooler and a second oxygen sensor positioned upstream ofthe charge air cooler with respect to one another. For example, if thesensors disagree with one another by greater than a maximum threshold,one and/or both of the sensors may be determined to be degraded, and anindication thereof may be generated, such as through a diagnostic codestored in memory of the controller. In one example, condensate less thanthe threshold forming in the charge air cooler is determined based on anestimate of an amount of condensate in the charge air cooler, theestimate based on each of mass air flow, ambient temperature, charge aircooler outlet temperature, charge air cooler pressure, ambient pressure,an exhaust gas recirculation amount, and humidity. In another example,condensate less than the threshold forming in the charge air cooler isdetermined based on an estimate of an amount of condensate in the chargeair cooler, the estimate based on charge air cooler outlet temperatureand a ratio of charge air cooler pressure to ambient pressure. Further,condensate less than the threshold leaving the charge air cooler isbased on one or more of an estimated amount of condensate in the chargeair cooler, mass air flow, humidity, and/or charge air coolertemperature.

The method may further include indicating degradation (e.g., diagnosingoutput) of the first oxygen sensor and the second oxygen sensor when anexhaust gas recirculation flow is less than a threshold, the thresholdbeing substantially zero. Degradation of one or more of the first oxygensensor and the second oxygen sensor may be indicated in response to theoutput of the first oxygen sensor not being within a threshold of theoutput of the second oxygen sensor. In one example, indicatingdegradation includes notifying a vehicle operation that one or moreoxygen sensors are degraded. Additionally, before indicatingdegradation, the method may include zeroing the first oxygen sensor andthe second oxygen sensor and then re-comparing outputs of the firstoxygen sensor and the second oxygen sensor in response to the output ofthe first oxygen sensor not being within a threshold of the output ofthe second oxygen sensor. In one example, the output of the first oxygensensor and the output of the second oxygen sensor include an oxygenconcentration of charge air.

FIG. 6 illustrates a method 600 for estimating the amount of condensatestored within a CAC. Based on the amount or rate of condensate formationin the CAC, oxygen sensor diagnostics, such as those discussed at FIG.5, may be executed.

The method begins at 602 by determining the engine operating conditions.These may include, as elaborated previously at 502, ambient conditions,CAC conditions (inlet and outlet temperatures and pressures, flow ratethrough the CAC, etc.), mass air flow, MAP, EGR flow, engine speed andload, engine temperature, boost, etc. Next, at 604, the routinedetermines if the ambient humidity is known. In one example, the ambienthumidity may be known based on the output of a humidity sensor coupledto the engine. In another example, humidity may be inferred from adownstream UEGO sensor or obtained from infotronics (e.g., internetconnections, a vehicle navigation system, etc.) or a rain/wiper sensorsignal. If the humidity is not known (for example, if the engine doesnot include a humidity sensor), the humidity may be set to 100% at 606.However, if the humidity is known, the known humidity value, as providedby the humidity sensor, may be used as the humidity setting at 608.

The ambient temperature and humidity may be used to determine the dewpoint of the intake air, which may be further affected by the amount ofEGR in the intake air (e.g., EGR may have a different humidity andtemperature than the air from the atmosphere). The difference betweenthe dew point and the CAC outlet temperature indicates whethercondensation will form within the cooler, and the mass air flow mayaffect how much condensation actually accumulates within the cooler. At610, an algorithm may calculate the saturation vapor pressure at the CACoutlet as a function of the CAC outlet temperature and pressure. Thealgorithm then calculates the mass of water at this saturation vaporpressure at 612. Finally, the condensation formation rate at the CACoutlet is determined at 614 by subtracting the mass of water at thesaturation vapor pressure condition at the CAC outlet from the mass ofwater in the ambient air. By determining the amount of time betweencondensate measurements at 616, method 600 may determine the amount ofcondensate within the CAC since a last measurement at 618. The currentcondensate amount in the CAC is calculated at 622 by adding thecondensate value estimated at 618 to the previous condensate value andthen subtracting any condensate losses since the last routine (that is,an amount of condensate removed, for example, via purging routines) at620. Condensate losses may be assumed to be zero if the CAC outlettemperature was above the dew point. Alternatively, at 620, the amountof condensate removed may be modeled or determined empirically as afunction of air mass and integrated down with each software task loop(that is, with each run of routine 600).

As such, the method of FIG. 6 may be used by the controller during theroutine of FIG. 5 to use a modeling method for estimating the amount ofcondensate at the CAC. In alternate embodiments, the engine controlsystem may use a mapping method to map the amount of condensate at theCAC to a CAC inlet/outlet temperature, an ambient humidity, and anengine load. For example, the values may be mapped and stored in alook-up table that is retrieved by the controller during the routine ofFIG. 5 (at 508), and updated thereafter.

FIGS. 7A-B show a graphical example of adjustments to engine operationbased on water storage at the CAC. Specifically, graph 700 shows changesin an output of a first oxygen sensor at plot 702, changes in an outputof a second oxygen sensor at plot 704, changes in CAC water storagebased on the oxygen sensor outputs at plot 706, changes in CAC waterstorage based on one or more condensate models at plot 708, changes inEGR flow at plot 712, changes in pedal position (PP) at plot 714,changes in spark timing at plot 716, changes in a position of vehiclegrille shutters at plot 718, changes is mass air flow at plot 720, andchanges in sensor degradation at plot 722. Graph 726 of FIG. 7B iscontinued from graph 700 of FIG. 7A. Both graph 726 and graph 700 havethe same time scale and time points referenced below. Graph 726 showschanges in oxygen measured at the outlet sensor when the outlet sensoris in the base mode (e.g., at the base reference voltage) at plot 728,changes in oxygen measured at the outlet sensor when the outlet sensoris in VVs mode (e.g., at the second, higher reference voltage) at plot730, changes in reference voltage at plot 732, and changes in pumpingcurrent of the outlet sensor at plot 734. The first oxygen sensor may bepositioned at an outlet of the CAC and referred to herein as the outletoxygen sensor. The second oxygen sensor may be positioned at an inlet ofthe CAC and referred to herein as the inlet oxygen sensor. In alternateembodiments, the CAC may only include one oxygen sensor at either theinlet or outlet of the CAC. For example, the CAC may only include theoutlet oxygen sensor. Additionally, the inlet and outlet oxygen sensorsmay be modulated between a first reference voltage, V1, and a secondreference voltage, V2. The first reference voltage may also be referredto as the base reference voltage. Plot 734 shows an example pumpingcurrent of the outlet oxygen sensor. The water concentration at theoutlet sensor may be based on the change in pumping current whenswitching between V1 and V2. Plots 728 and 730 show example oxygensensor readings at the outlet sensor during operation at base mode andVVs mode, respectively. Similar changes in pumping current may occur atthe inlet oxygen sensor (not shown).

Plot 706 shows changes in water storage in the CAC, the water storagebased on the outputs from the inlet oxygen sensor and the outlet oxygensensor. The water storage shown at plot 706 may include an amount ofwater stored in the CAC or a rate of water storage in the CAC. Plot 708also shows water storage data based on one or more condensate models. Inone example, the water storage at plot 708 may include an amount or rateof water storage estimated from the condensate model shown at FIG. 6.

Prior to time t1, water storage in the CAC may be less than a thresholdT1 (plot 706) and water release from the CAC may be less than athreshold T2 (plot 710). Additionally, the pedal position may berelatively constant (plot 714) and the grille shutters may be closed(plot 718). Before time t1, the inlet oxygen sensor output may beincreasing. In one example, the inlet oxygen sensor output may be anoxygen concentration or estimated amount of oxygen in the charge air.This may indicate an increased amount of water in the charge airentering the CAC. As a result, the CAC water storage level may beincreasing before time t1 (plot 706). Also before time t1, the referencevoltage of both the inlet oxygen sensor and the outlet oxygen sensor maybe modulated at a first rate (plot 732). The oxygen sensors may beoperating at the second reference voltage (in VVs mode) for a firstduration d1. Additionally, the difference between the oxygenconcentration measured in VVs mode (plot 730) and the oxygenconcentration measured in the base mode (plot 728) may be the net outletoxygen sensor output, as shown at plot 702.

At time t1, the CAC water storage level increases above the threshold T1(plot 706). In response, the controller may close the grille shutters(plot 718) to reduce condensate formation in the CAC. In alternateexamples, the controller may adjust alternate or additional engineactuators to reduce condensate formation. For example, the controllermay additionally or alternatively turn off an engine cooling fan at timet1.

Between time t1 and time t2 EGR flow increases slightly (plot 712). As aresult, the pulse width, or rate of modulation decreases to a secondrate (plot 732). Between time t1 and time t1 the CAC water storage levelmay decrease. At time t2, the CAC water storage may decrease below thethreshold T1 (plot 706). In response, the controller may re-open thegrille shutters (plot 718). In alternate embodiments, the grilleshutters may remain open at time t2. Also before time t2, mass air flowbegins to increase. In one example, the controller may increase mass airflow based on engine operation. In another example, the controller mayincrease mass air flow to purge the stored condensate from the CAC. Asthe mass air flow increases, the outlet oxygen sensor output alsoincreases. This increase in output may indicate an increase in water inthe charge air exiting the CAC. As a result, water release from the CACmay be increasing between time t2 and time t3 (plot 710). At time t3,the CAC water release increases above threshold T2. In response, thecontroller retards spark timing from MBT (plot 716). The controller mayretard spark timing rather than advancing spark timing since pedalposition remains relatively constant at time t3. Retarding spark duringthe water release from the CAC may increase combustion stability as theengine ingests the released water (e.g., condensate). At time t4 thewater release from the CAC decreases below the threshold T2 (plot 710).The controller then stops retarding spark (plot 716).

Between time t4 and time t5, EGR flow may decrease below a threshold T3.As EGR flow decreases, the rate of modulation between V1 and V2, and thepulse width of the modulation, increases to a third rate (plot 732). Inone example, the threshold T3 may be substantially zero such that theEGR is turned off. In another example, the threshold T3 may be a flowrate greater than zero. Once EGR decreases below the threshold T3, theoutlet oxygen sensor and the inlet oxygen sensor may stay at the secondreference voltage V2 and operate solely in VVs mode. In other examples,the oxygen sensors may continue to switch between operating at the firstvoltage and the second voltage, but the rate of modulation may be slowerthan previous rates wherein EGR was greater than zero.

Also between time t4 and time t5, the water storage in the CAC, based onthe condensate model, may decrease below a threshold (plot 708). In oneexample, the threshold may be substantially zero. As a result, it may beinferred that no condensate is forming in the CAC. Based on engineoperating conditions, the controller may also determine that nocondensate is leaving the CAC (e.g., condensate less than a threshold isleaving the CAC). During engine operation wherein no condensate (orcondensate less than a threshold) is forming in and leaving the CAC, theoutlet oxygen sensor and the inlet oxygen sensor may have similaroutputs. However, at time t5, the inlet oxygen sensor output and theoutlet oxygen sensor output may deviate from one another by a threshold,the threshold indicated at 724. As a result, the controller may indicatesensor degradation, as shown at plot 722. Indicating sensor degradationmay include indicating that one or more of the inlet oxygen sensor andthe outlet oxygen sensor are degraded. In one example, the controllermay notify the vehicle operator of sensor degradation at time t5.

In this way, outputs from one or more oxygen sensors positionedproximate to a CAC outlet and/or a CAC inlet may be used to determinewater storage at the CAC. In one example, an oxygen sensor positioned atthe outlet of the CAC may be used to determine the presence and/or anamount of water in the charge air exiting the CAC. In another example, afirst oxygen sensor positioned at the outlet of the CAC and a secondoxygen sensor positioned at the inlet of the CAC may be used todetermine one or more of an amount of water leaving the CAC (e.g., waterrelease amount), a rate of water leaving the CAC (e.g., water releaserate), an amount of water within the CAC (e.g., water storage amount),and or a rate of water accumulation within the CAC (e.g., water storagerate). A controller may adjust one or more engine actuators in responseto one or more of the above CAC water storage parameters. For example,the controller may adjust vehicle grille shutters, engine cooling fan,and/or an engine coolant pump to reduce CAC cooling efficiency inresponse to a water storage amount or rate above a threshold. In anotherexample, the controller may adjust spark timing and/or engine airflow(or mass air flow) in response to the water release amount and/or waterrelease rate increasing above a threshold. In yet another example, thecontroller may adjust engine airflow via adjusting a throttle and/ordownshifting operations to purge condensate from the CAC in response tothe water storage amount increasing above a threshold. In this way, atechnical result of determining water storage parameters of the CAC fromone or more oxygen sensors may be achieved, thereby reducing CACcondensate formation and increasing combustion stability.

As one embodiment, an engine method may include adjusting engineactuators based on water storage parameters at a charge air cooler, thewater storage parameters based on an output of a first oxygen sensorpositioned at an outlet of the charge air cooler. The water storageparameter includes an amount of water in charge air exiting the chargeair cooler. Further, adjusting engine actuators includes one or more ofadjusting spark timing and limiting engine airflow responsive to theamount of water in the charge air exiting the charge air coolerincreasing above a threshold amount. The amount of water is estimatedbased on a pumping current of the first oxygen sensor and a saturationwater value at an outlet temperature condition of the charge air cooler.In one example, adjusting spark timing includes advancing spark timingwhen a pedal position is increasing. In another example, adjusting sparktiming includes retarding spark timing when the pedal position is belowa threshold position.

The water storage parameters may further include a water release ratefrom the charge air cooler, a water storage rate at the charge aircooler, and a water storage amount at the charge air cooler. The waterrelease rate, the water storage rate, and the water storage amount arebased on the output of the first oxygen sensor and an output of a secondoxygen sensor positioned at an inlet of the charge air cooler. In oneexample, adjusting engine actuators includes one or more of adjustingspark timing and mass air flow in response to the water release rateincreasing above a threshold rate. In another example, adjusting engineactuators includes one or more of adjusting vehicle grille shutters,engine cooling fans, and a charge air cooler coolant pump to decrease acooling efficiency of the charge air cooler in response to the waterstorage rate increasing above a threshold rate. In yet another example,adjusting engine actuators includes increasing engine airflow to purgecondensate from the charge air cooler in response to the water storageamount increasing above a threshold amount.

As yet another embodiment, an engine method may include adjusting engineoperation and generating diagnostics responsive to water storageparameters at a charge air cooler, the water storage parameters based onan output of a first oxygen sensor positioned downstream of the chargeair cooler and an output of a second oxygen sensor positioned upstreamof the charge air cooler. Specifically, the first oxygen sensor may bepositioned at an outlet of the charge air cooler and the second oxygensensor may be positioned at an inlet of the charge air cooler. Themethod may further include modulating a reference voltage of the firstoxygen sensor and the second oxygen sensor between a first voltage and asecond voltage, the second voltage higher than the first voltage. Themethod further includes modulating the reference voltage of the firstoxygen sensor and the second oxygen sensor at a rate based on exhaustgas recirculation flow, the rate increasing with increasing exhaust gasrecirculation flow. In some embodiments, the method further includesmaintaining the first oxygen sensor and the second oxygen sensor at thesecond voltage when exhaust gas recirculation flow is substantiallyzero.

Water storage parameters at the charge air cooler include one or more ofa water release amount from the charge air cooler, a water release ratefrom the charge air cooler, a water storage amount in the charge aircooler, and a water storage rate in the charge air cooler. Adjustingengine operation includes one or more of adjusting spark timing and massair flow in response to one of the water release amount increasing abovea threshold amount or the water release rate increasing above athreshold rate. Adjusting engine operation may also include one or moreof adjusting vehicle grille shutters, engine cooling fans, and a chargeair cooler coolant pump to decrease a cooling efficiency of the chargeair cooler in response to the water storage rate increasing above athreshold rate. Adjusting engine operation may further includeincreasing engine airflow to purge condensate from the charge air coolerin response to the water storage amount increasing above a thresholdamount. Additionally, generating diagnostics includes one or more ofdiagnosing function of the first oxygen sensor and the second oxygensensor and/or diagnosing errors in a charge air cooler efficiency andcondensate model.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. An engine method, comprising: during engine operation when condensate less than a threshold is forming in a charge air cooler and condensate less than the threshold is leaving the charge air cooler, indicating degradation of a first oxygen sensor positioned downstream of the charge air cooler and a second oxygen sensor positioned upstream of the charge air cooler with respect to one another.
 2. The method of claim 1, wherein condensate less than the threshold forming in the charge air cooler is determined based on an estimate of an amount of condensate in the charge air cooler, the estimate based on each of mass air flow, ambient temperature, charge air cooler outlet temperature, charge air cooler pressure, ambient pressure, an exhaust gas recirculation amount, and humidity.
 3. The method of claim 1, wherein condensate less than the threshold forming in the charge air cooler is determined based on an estimate of an amount of condensate in the charge air cooler, the estimate based on charge air cooler outlet temperature and a ratio of charge air cooler pressure to ambient pressure.
 4. The method of claim 1, wherein condensate less than the threshold leaving the charge air cooler is based on one or more of an estimated amount of condensate in the charge air cooler, mass air flow, humidity, and charge air cooler temperature.
 5. The method of claim 1, further comprising indicating degradation of the first oxygen sensor and the second oxygen sensor when an exhaust gas recirculation flow is less than a threshold, the threshold being substantially zero.
 6. The method of claim 5, further comprising indicating degradation of one or more of the first oxygen sensor and the second oxygen sensor in response to the output of the first oxygen sensor not being within a threshold of the output of the second oxygen sensor, and wherein indicating degradation includes notifying a vehicle operator that one or more oxygen sensors are degraded.
 7. The method of claim 6, further comprising, before indicating degradation, zeroing the first oxygen sensor and the second oxygen sensor and then re-comparing outputs of the first oxygen sensor and the second oxygen sensor in response to the output of the first oxygen sensor not being within a threshold of the output of the second oxygen sensor.
 8. The method of claim 1, wherein the output of the first oxygen sensor and the output of the second oxygen sensor include an oxygen concentration of charge air.
 9. An engine method, comprising: adjusting engine operation responsive to water storage parameters at a charge air cooler, the water storage parameters based on an output of a first oxygen sensor positioned downstream of the charge air cooler and an output of a second oxygen sensor positioned upstream of the charge air cooler.
 10. The method of claim 9, wherein the first oxygen sensor is positioned at an outlet of the charge air cooler and the second oxygen sensor is positioned at an inlet of the charge air cooler.
 11. The method of claim 9, further comprising modulating a reference voltage of the first oxygen sensor and the second oxygen sensor between a first voltage and a second voltage, the second voltage higher than the first voltage.
 12. The method of claim 11, further comprising modulating the reference voltage of the first oxygen sensor and the second oxygen sensor at a rate based on exhaust gas recirculation flow, the rate increasing with increasing exhaust gas recirculation flow.
 13. The method of claim 11, further comprising maintaining the first oxygen sensor and the second oxygen sensor at the second voltage when exhaust gas recirculation flow is substantially zero.
 14. The method of claim 9, wherein water storage parameters at the charge air cooler include one or more of a water release amount from the charge air cooler, a water release rate from the charge air cooler, a water storage amount in the charge air cooler, and a water storage rate in the charge air cooler.
 15. The method of claim 14, wherein adjusting engine operation includes one or more of adjusting spark timing and mass air flow in response to one of the water release amount increasing above a threshold amount or the water release rate increasing above a threshold rate.
 16. The method of claim 14, wherein adjusting engine operation includes one or more of adjusting vehicle grille shutters, engine cooling fans, and a charge air cooler coolant pump to decrease a cooling efficiency of the charge air cooler in response to the water storage rate increasing above a threshold rate and wherein adjusting engine operation includes increasing engine airflow to purge condensate from the charge air cooler in response to the water storage amount increasing above a threshold amount.
 17. The method of claim 9, further comprising indicating degradation of the first oxygen sensor and the second oxygen sensor and diagnosing errors in a charge air cooler efficiency and condensate model based on the output of the first oxygen sensor and the output of the second oxygen sensor.
 18. An engine system, comprising: an intake manifold; a charge air cooler positioned upstream of the intake manifold; a first oxygen sensor positioned at an outlet of the charge air cooler; a second oxygen sensor positioned at an inlet of the charge air cooler; and a controller with computer readable instructions for adjusting engine operation responsive to water storage parameters at the charge air cooler, the water storage parameters based on an output of the first oxygen sensor and an output of the second oxygen sensor.
 19. The system of claim 18, wherein adjusting engine operation includes one or more of adjusting spark timing, mass air flow, vehicle grille shutters, engine cooling fans, a charge air cooler coolant pump, and/or downshifting a transmission gear and wherein water storage parameters include one or more of a water release amount from the charge air cooler, a water release rate from the charge air cooler, a water storage amount in the charge air cooler, and a water storage rate in the charge air cooler.
 20. An engine method, comprising: adjusting engine operation responsive to water content in an intake system, the water content based on an output of an intake oxygen sensor wherein a reference voltage of the intake oxygen sensor is adjusted between a first voltage and a second voltage at a higher rate as an exhaust gas recirculation flow increases. 